Alumina-chromia-molybdena catalyst



Dec. 11, 1956 w. A. STOVER 2,773,846

ALUMINA-CHROMIA-MOLYBDENA CTALYST Filed June 13, 1952 Y/ELD, 10111. EVP Rim/warf, WL.

L IN VEN TOR.

Milzm .Sidi/ef HTOR/VEY United States Patent O ALUMlNA-CHROMIA-MOLYBDENA CATALYST William A. Stover, Pitman, N. J., assignor to Socony Mobil Oil Company, Inc., a corporation of New York Application June 13, 1952, Serial No. 293,412

2 Claims. (Cl. 252-465) This invention relates to an improved catalytic reforming process for obtaining gasoline of high octant number. More particularly, the present invention is directed to catalytic reforming carried out in the presence of a catalyst consisting essentially of a co-gelled chromia-alumina composite of particularly dened composition impregnated with a specified amount of molybdena and to a process for preparing such catalyst.

Reforming operations wherein saturated gasoline fractions comprising straight run gasolines, natural gasolines, etc., are treated to improve the anti-knock characteristics thereof are Well known in the petroleum industry. Straight run gasolines generally contain naphthenic hydrocarbons, particularly cyclohexane compounds and paraflinic hydrocarbons which are usually of straight chain or slightly branch chain structure, as well as varying proportions of aromatic hydrocarbons. During reforming, a multitude of reactions take place, including isomerization, dehydrogenation, cyclization, etc., to yield a product of increased aromatic content. Thus, in reforming, it is desired to dehydrogenate the naphthenic hydrocarbons to produce aromatics, to cyclisize the straight chain paratnic hydrocarbons to form aromatics, and to effect a controlled type of cracking which is selective both in quality and quantity.

Controlled or selective cracking is highly desirable during reforming since such will result in a product of anti-knock characteristics. As a general rule, the lower molecular weight hydrocarbons exhibit a higher octane number, and a gasoline product of lower average molecular weight will usually have a higher octane number. In addition, the isomerization and molecular rearrangement which occur during reforming also result in products having higher anti-knock characteristics. The splitting or cracking of carbon to carbon linkages must, however, be selective and should be such as not to result in substantial decomposition of normally liquid hydrocarbon into normally gaseous hydrocarbons. The selective cracking desired ordinarily involves removal of one or two lower alkyl groups, such as methyl or ethyl, from a given molecule in the form of methane or ethane. Thus, during reforming, it is contemplated that heptane may be converted to hexane, nonane to octane or heptane, etc. Uncontrolled cracking, on the other hand, would result in decomposition of normally liquid hydrocarbons into normally gaseous hydrocarbons. For example, nonselective cracking of normal octane would ultimately lead to eight molecules of methane.

Uncontrolled reforming, moreover, generally results in rapid formation and deposition on the catalyst of large quantities of a carbonaceous material generally referred to as coke The deposition of coke on the catalyst surface diminishes or destroys its catalyzing effect and results in shorter processing periods with the accompanying necessity of frequent regeneration by burning the coke therefrom. In those instances where the activity of the catalyst is destroyed, it is necessary to 2,773,846 Patented Dec. 11, :6

ICC

selected should further be resistant to poisoning and particularly to sulfur poisoning so that sulfur-containing stocks may undergo reforming without the necessity of subjecting the same to a preliminary treatment for desulfurization. The catalyst also should desirably be characterized by high stability and be capable of easy regeneration, and the method for preparing such catalyst should be commercially attractive, requiringv a minimum of equipment and processing stages.

In accordance with the present invention, a catalyst of the above-defined characteristics has been discovered. Broadly, the present invention comprises reforming a naphtha fraction of petroleum in the presence of a catalyst consisting essentially of co-gelled chromia and alumina impregnated with a critical minor proportion of molybdena. The invention further comprises a method for preparing the catalystunder conditions such that a completely homogeneous active surface is obtained.

It has heretofore been proposed to employ composites containing two or more of the oxides of chromium, aluminum, and molybdenum as catalysts for various reactions. Several methods for preparing such catalysts have been proposed, including alternate impregnation of an alumina support with suitable chromium and molybdenum compounds and co-precipitation of solutions containing salts of the desired metals. The diiculties encountered in the former method are well known in that a completely homogeneous active surface is seldom attained even when tedious methods are used. The latter technique, while overcoming this difficulty, is even more involved and requires extremely close control of pH and other variables to assure satisfactory results. Chromia-alumina composites heretofore recommended as reforming catalysts have been found to be characterized by a certain amount of instability, as indicated by the amount of CrzOa converted to the crystalline form during use. Catalysts of the present invention consisting essentially of co-gelled chromia-alumina impregnated with molybdena have been found to have an improved stability in comparison with the aforesaid chromia-alumina composites and have, further, been found to have improved reforming activity in comparison with'chromia-alumina composites or molybdena-alumina composites.

The method of reforming naphtha fractions of petroleum in the presence of a co-gelled chromia-alumina composite impregnated with molybdena as described herein has been found -to have cetrain advantages over the processes commercially available. The advantages obtained upon reforming with the present catalyst, while not fully understood, are believed to result from the method of preparation of the catalyst employed. The instant method of catalyst preparation involves the formation of a hydrogel of chromia and alumina preferably containing a chromia-alumina content `of at least l0 percent by weight and thereafter irnpregnating either the washed hydrogel or the dried and tempered material with a solution of a water-soluble molybdenum compound. A preferred embodiment of the invention involves the formation of co-gelled aluminum and chromium oxides which, after drying and/or tempering, areevacuated toa reduced pressure. The evacuated chromia-alumina gel,

a'nti-knock properties.

generally in particle form,k is then brought into contact with a solution of a water-soluble molybdenum compound. Molybdic acid or-*the alkaline salts thereof are preferred for-such purpose. Theconcentration ofthe Water-soluble molybdenum compound ,in the impregna'tng YDuring this .heating treatment, it is desirable that the 'atmosphere 'surroundin'gthe material be free of oxygen. Such fan atmosphere is Yprovided in a preferred-embodime'ntfof vthe .invention by 'permitting the steam produced during Tthecours'e .of heating'from' the moisture contained fin 'the 'catalyst 'after impregnation to blanket the catalyst mass. n lThe impregnated 'dried Acatalyst consisting essen- 't'ially 'of 'a co-ge'l 'of alumina andchromia Vimpregna-ted withmolybdenum oxide is thereafter ready for'use.

Composites consisting of a major proportion of `alumina, a minor proportion of chromia, and a'minor proportionof molybdena are suitably prepared by the method Vof the invention. Catalysts having a -composition of to 30percent by weightof chromia, 50 to 89 percent by 'weight 'of alumina, and 1 to 2O per-cent Vby Weight of molybde'na are unusually effective for promoting reformv:ingop'erations in which a saturated gasoline is subjected to conversion to produce a reformed gasoline of improved Catalysts having a molybdena concentration inthe range of 8 to 12 percent are particularly preferred in Vthe present invention. Thus, a com- 'posite'havinga composition inthe range of20 to 30 percent chromia, 58 to 72 percent alumina, and 8 to 12 percent molybdena, in which chromia and alumina in the "form of'a co-gel a're impregnated with molyb'dena, repre- "sents a preferred embodiment of theinvention and Ahas been found totafford an improved yield 4of Vreformate of "the sameroctane number as compared to' an operation vvcarriedout under'identical reforming Yconditions employing '-a chromia-alumina gel catatlyst of corresponding 'composition lbut which' had not been impregnated with molybdena.

The method ofthe invention Iprovides a simple 'but highly effective' procedure for preparation'of molybdenacOntaining reforming catalyst. The co-gel of chromiaalumi'na is a true gel prepared by forming `a'hydrosol'of @chromia and alumina, 'permitting said hydrosol 'to setto an all-embracing hydrogel and thereafterdrying the l`hydrogel. The gel, as indicated above, is suitably, but

not necessarily, in particle-form prior to impregnation. Theparticlesmay be of irregularsize such as those prodi1`c'ed'1b'y'y breaking up V`a'previously set dried ngel 'or the particles may bei in the 'form of extruded or pressed-pellets. Preferably, however, the alumina-chromia gel particles are in the form of spheroids preparedbyintroducingthe hydrosol in the form of globules into a water-immiscible 'medium v-Wherein the hydrosol globules set to spheroidal l'hydrogel particles which are thereafter removed and dried to formfhard gel spheroids highly resistant to attrition.

:It i'sfparticularly 'preferred to prepare a co-gelled cataiopereenrby weight'anda relatively-short gelation'time, i.'e;,` less'tha'nZhours and Vpreferably less Atl1'arr60` seconds,

is prepared by intimately admixing an organic chromium salt, 'such as chromic acetate, and an alkali metalaluminate, such as sodium aluminate to produce a chromiaalumina hydrosol. The hydrosol so formed is permitted to set to a hydrogel. The resulting hydrogel is thereafter subjected to aging and then Water-washed, dried, and calcined to yieldacatalytic chromia-alumina gel composite. The relative proportions of chromia land alumina may be variedrover-a wide range. In accordance with the instant invention, however, the concentrations of reactants employed shouldbesuchasto afford a chromia-alumina gel of composition Within the range set forthhereinabove.

It is preferred, in preparing the above-described hydrogels, to use aqueous solutions ofso'dium aluminate and chromic acetate. Neither of these substances is a true chemical compound. The ratio of sodium to aluminum can be varied Widely as can the ratio of acetate to chromiumion. Variation in the sodium .to aluminum ratio of the aluminate solution requires compensating adjustment of the acetate to chromium ratio of the second solutionin -orderto achieve 'satisfactory gelation. Hydrosols capable of setti-ng to .hydrogels'in Ile'sszthan Vabout `20 seconds are particularly "desirable for the production of Vbead-'like spheroidal particles bypmethod's wellfknown in the art, for example, those' 'described in patents yto vMarisic, such as U. S. Patent No. 2,384,946.

Quick-setting hydrosols of low'viscositywhich can'be readily handled at 'bead-'forming nozzles 'are 'those prepared 'from' sodium'aluminatesolutions which :have a sodium to aluminum mole ratio-referred'to as R*ofbe `twee'n'l and '1.5. The acetate y'to chromium mole "ratio `in the chromic acetate srolution'employed should'be' not less than 2.8R1;8 an'clnot morethan 4R-2.-4"and preferably'in the range of 11R-'27.8 to `4R-2.Li.

The control of the mole ratios discussed above' is readily achieved in the manufacture of reactantsolutions. 'Chromium lacetate is" readily "formed Without introduction -ofundesirab'leextraneous 'materials by 'reducing sodium Vdichromatewith glycolic'acid inthe presence of' acetic acid Vasy described more rfullyi'n my copending applicationSerial No; 174,594, ledflul'y -18, 1950, vnow U. S. 22611031, issued October 21, 1.952. Y

Sodium aluminate is convenientlyjprepared from'causticrs'oda of-'50` lBe. and "alumi'numtrihydrate. Ata'sodium to aluminum mole lratio lintl'ie range-'of`1'.25'/'1 to 1.5/1, the sodium/aluminate is `advantageouslymanufactured in an open agitated kettle-at220-23'0 F. witha reaction time of 1 to 3 hours. Solutionshaving Va' lower mole ratio down to about 1.0/1 are made'in' an autoclave at -240'-300 F. and V10 Ato 30 pounds per square inch gauge at the same reaction time. "Sodium aluminate 'solutions having a low "sodium to .aluminate 'ratio less than 1.3 are relatively unstable andmay bestabilized by `the"addition of such organic materials as glycerin@ starch, sugar, and the like.

Thus,V chromia-alumina hydrogels having ra-.short .time of fset and avhigh solids-contentgenerally between-about 10 and v'about 30 percent by Weight mayreadily'be'preparedby controlling-the sodium to aluminurnfmoleiratio of the 1sodium ialuminatesolution employed v and the .acetate to chromium ltmole ratio 4of f the` Vchromic acetate .Iso-

Vlution. .The specicratiosemployed willfldepend upon Sthe 'particular -composition of the' chr'orma-aluminav hydrogel desired.

Temperature, acidity, andproductconcentration are interrelated 4variables effecting' gelation 'and within the llimits in which `format-ion; of 'hydrogels occurs they con- F."arei suitable. :Best-"gelation times 4are :iexperience'dat pH 'ofV 4*the chromia=alumina hydrogels isf"generall'y 'bearras-1e tween l and i3. For bead formation, a pH of about l2 yields excellent results.

For the production of chromia-alumina hydrogel beads, preparation is carried out substantially the same as that described in the above noted Marisic patent for producing silica-alumina beads. Thus, a chromium acetate solution and a sodium aluminate solution are coutacted in a mixing nozzle and discharged onto the apex of a dividing cone from which a number of small streams ow into a column of water-immiscible liquid. r[he temperature of said water-immiscible liquid is desirably maintained constant by circulation through a heat exchanger outside the bead-forming tower.

The freshly formed chromia-alumina hydrogel above described is subject to a loss of aluminum as sodium aluminate if immediately washed with water. This tends to weaken the hydrogel to such an extent that it disintegrates in the Wash water. That adverse eifect can be avoided by immediately treating the freshly formed hydrogel in a slightly alkaline aqueous medium. This is generally accomplished by bringing the freshly formed chromia-alumina hydrogel into contact with an aqueous solution of an ammonium salt of a mineral acid or a mineral acid or a mixture of such salt and acid. In a typical operation, the freshly formed hydrogel beads are sluiced out of the forming tower with oil. The hydrogel beads are then separated from the oil and treated with a 20 percent by weight solution of ammonium sulfate. rl'he solution is advantageously kept at a pH of 8.0 to 9.5 by the addition of sulphuric acid. It is advisable to maintain a solution of this type in contact with the freshly formed hydrogel for some time after formation. For example, the solutionjs' recirculated through the freshly formed hydrogel or otherwise maintained in Contact therewith for a period of from about 2 to about 24 hours after forming in order to fix the alumina. Such treatment of the freshly formed hydrogel is designated herein as aging After the aging treatment, the chromia-alumina hydrogel is water-washed free of anions introduced during aging. The washed hydrogel can be satisfactorily dried in either superheated steam or heated air. Hydrogels so dried may be tempered at an elevated temperature generally in the range of 500 F. to l200 F. in an inert or reducing atmosphere, such as ue gas.

The resulting particles of chromia-alumina gel are evacuated to a reduced pressure of generally less than mm. of mercury and preferably less than 2 mm. of mercury. Evacuation of the gel particles serves a twofold purpose. First, it assures substantial removal of air from the pores of the gel which, if permitted to remain, would cause breakage of the gel particles when the same are subsequently contacted with aqueous impregnating solution. Second, evacuation of the gel particles affords a uniform and rapid distribution of the impregnating solution throughout the evacuated particles and thus provides a uniform, active surface of molybdena on the chromia-alumina gel. l

The gel particles in evacuated condition are brought into contact with an aqueous solution of a water-soluble molybdenum compound. A solution of molybdic acid or ammonium molybdate is preferred for such purpose although the alkaline salts of this acid or other readily available molybdenum-containing compounds which are soluble in water may likewise be used. The concentration of the impregnating solution may be Varied depending upon the composition of the catalyst desired. Suflicient solution is used to cover the chromia-alumina gel particles during impregnation. The particles are permitted to remain in contact with the impregnating vsolution for a length of time suicient to permit the solution to impregnate the chromia-alumina gel. Under the usual conditions contemplated for impregnation, this time Will generally range from one second up to about ten minutes.

At the completion 'of the impregnation, the catalyst is removed from the vacuum chamber and the wet impregnated particles are slowly heated to an elevated temperature in the range of 800 to 1000 F. The rate of such heating should be comparatively slow, generally not in excess of 10 F. per minute. During the period of heating the wet catalyst particles, the atmosphere surrounding such particles should be desirably free of oxygen. This may be accomplished by maintaining an inert atmosphere in contact with the particles during the course of heating. In a preferred embodiment of the invention, a non-oxidizing atmosphere may be provided by permitting the steam produced from the moisture contained in the wet catalyst to blanket the mass of particles being heat-treated. The resulting catalyst is a composite consisting essentially of the chromia-alumina gel impregnated with an effective amount of molybdena.

The evacuation, impregnation and subsequent heat treatment of the chromia-alumina gel particles in accordance with this invention may be carried out either as a batch or continuous operation. Thus, the chromiaalumina gel particles after evacuation may be permitted to contact the molybdic acid or other impregnating solution under substantially static conditions for the requisite time or the gel particles may be passed through a solution of the impregnating solution or, alternatively, the impregnating solution may be circulated through a stationary bed of the gel particles. Likewise, contact between the impregnating solution and the chromia-alumina gel particles may be accomplished by countercurrent passage thereof through an elongated treating zone. Heat treatment of the impregnated particles may also be effected as a batch or continuous operation. An alternate method of preparation for the cogelled chromiaalumina composite impregnated with molybdena as described herein involves contacting the aged, water-washed chromia-alumina hydrogel prepared as hereinabove described with an aqueous solution of a water-soluble molybdenum compound such as molybdic acid or the alkaline salts thereof. In this method of operation, the period of impregnation will generally be within the range of 2 to 48 hours. The impregnated composite is thereafter dried preferably in superheated steam at a temperature of 220-250 F. and subsequently tempered at an elevated temperature of about l000 F. Also, in some1 instances, it may be desirable to prepare the catalyst by purging the dried, tempered chromia-alumina gel particles under atmospheric pressure with steam at a temperature above 212 F., thereby replacing the air which normally occupies the gel pores with steam. The gel particles so treated may then be brought into contact with the aqueous impregnating solution of molybdenum compound without encountering gel breakage and impregnation thereafter effected as in the case of the above-described evacuated particles.

The advantage of the present catalyst and procedures of preparation over those of the prior art is that a homogeneous, active catalytic surface is obtained and that the stability of the resultant three-component composite is distinctly improved as compared with chromia-alumina composite which had not been impregnated with molybdena. Thus, the catalyst described herein, comprising an intimate composite of alumina, chromia, and molybdena in specified amounts possesses both greater selectivity, activity, and stability than does a chromia-alumina composite of corresponding composition which had not undergone impregnation with molybdena. It would appear that the advantages derived in reforming with the present catalyst are due to the specic promoting eect of the specied quantities of molybdena when the same are combined with chromia-alumina gel of the aboverecited composition range.

Selectivity in a reforming catalyst is highly desirable since it further increases the octane number of the reformed gasoline, produces a gasoline of highervolatility and-eonverts higher; boilingfractions to lower boiling fractions within. the; range of; gasoline. catalysts. of the present invention are. particularly de.-

sirable for reforming operationsfusing a wide variety yoftA stocks. because the catalyst isunaiected by thepresence.v

of sulfur and is capableof effecting the desired aromatization;A and controlledf cracking' under selected conditions of operations.

Vfhile certain .details referred to in the foregoing description have ,been directed to .catalyst preparation in which chromia-,alumina gel is employed in the form of spheroidal particles, it is to be realized that it is within the purview'of this inventionA to use chromia-alumina gels Voff anyother desired former-shape.

The Y following. non-limiting' illustrative examples will serve to more specifically point outthe process of the invention Vand the improvedresults Yin activity and sta-y bility obtained with the-,catalyst=preparedin accordance with said process.

Example I. A chroinia-alumina hydrogel was prepared from the following reactants:

Solution A: 47.3 poundssodium aluminate made up to a volume of 10 gallons with distilled water;

Solution B: 48 pounds chromic acetate, the acetate to chromium ratio of which is adjusted within the approximate range of 2.6 to 2.8 and thenmade up to a volume of 13 gallons with distilled water, providing a solution containing 0.92A mole CrzOs per liter. Solutions A and B were pumped separately under pressure through heating coils to van efficient mixing nozzle.

Thesolutions were heatedto about 110 F. andmixed in equal Volumes at a ktotal ratev of 1200 cc. per minute...

The resulting stream of hydrosol ilowed overl a divider intoa column of D. T. E. (diesel turbine engine) light oil.

The hydrosel set to. beads of hydrogel and the resulting` necessary to add sulfuric acid to the sluicing solution in. orderto maintain the. pH a t;8.5.\ Thebeadhydrogel was.` aged for 24 hours in the same solution that was usedV to: sluice from the forming tower.V After aging, the gel wasZ washed until a sulfate-free wash Water. was indicated. The washed hydrogel had a product concentration of"2 1 percent by weight.

then Atempered. 4 hours ,at 1100 F. in a hydrogen atmos-i phere. The resulting beads of gel. contained approximately 32 percent by weight ofvchrornia. and .68' percent`r by weight` of alumina.

One thousand grams of the above-described chromia'.y alumina gel beadswere placed, in a suitable chamberand evacuated to a pressure-of 2mm. of mercury. An aqueous solutionof .494 grams of ammonium molybdate solution` having a concentration of 23. .percent by weight ofMoOs was then introduced into the chamber. The `gelbeads were permitted to remainincontact with the ammonium molybdate solution. foreaperiod between l andy 60 'seconds, after. whichtthe, impregnated gelbeadswere re. moved from. the vacuum chamber. and' slowlyv heated` to 1000 'R over a period of 25.0.1'ninutesfV During the. heating period, the atmosphere surrounding the Vimpregnated gel particles was maintainedffree of oxygen by permitting steamy from themoisture contained in. the catalyst Yto The4 resulting, catalyst' blanketthe mass of gelparticles. had the following composition:

Chromia, percentV weight v 28.8.` Alumina, percent weight 61.2v- Molybdenapereent weigh t 10.0

Example 2! A chroma-alumna lhydregei 'was 'prepare'fby ya-preeefy The improved.V

Y The. hydrogel Was-thereafter dried. in 100 percent steamy at 26o-270 F. for to 4 hours and.

dure;,lsim.1ar to that. of .EXample. l; Therhydrogel after aging was water-washed until a sulfate-free wash-.Waren wasindicated. TheI washed hydrogel had a product concentration of 18,per.cent by weight.`Y

Thewashedfhydrogel (8,640 grams)'was brought into: contact-.withg6g520 grams of molybdic acid solution having-a concentration of 3.8 percent by weight of M003. The Yhydrogel was'perrnitted to remain in contact with the molybdicl acid solution for -a period'of 24 hours, after whichthe impregnated hydrogel product Vwas removedy fromr the,v impregnatingf` solution, dried in superheatedsteamtor 5 hours Vat 233-240 F., and thereafterA tempered for 3 hoursat 1000 F.V The resulting catalyst had the ffollowllg 1 composition:

Chromia, percentv'weight 24.6 Alumina, percent weight 65.4; Molybdena, percent weight 9.0

The catalyst vof'EXample 1 together with a similarly i preparedv catalyst but containing 5 percent molybdena (30.4 percent Cr203--64.6 percent Al203-5;0 percentv4 M003), a chromia-aluminacogel prepared as describedA inEXample-l but notimpregnated with molybdena(32 percentCrzOz-f-SA percent A1203), and a catalyst consisting essentiallyi of molybdena on alumina. (10 'per- Y cent--Mo0a'-90'percent A1203) were tested in reforml ing a--naphthapetroleum `fraction under the followingy conditions:

Liquid hourly space velocity 1` Time lon stream','hours 2 Recycle to knaph'tha mole ratio 6.0V Hydrogento hydrocarbon mole ratio 4 Total pressure,.pr s. i; g. 175

The results, `obtained in this operation arer shown graphically in. the attached drawing for the above-described catalysts-. Referring more particularly. to the drawing .showing the .yield-.octane number relationship, it will be noted that at the 98 octane (CFRR-i-3 cc..TEL) level the .cogelled chromia-alumina catalyst impregnated with.l0 percentby weightmolybdena- (Example 1) produced a;yield. advantage. of v5.5 percent volume as come pared with chromia-alumina composite. and a .4 percentl that required for chromia-alumina `was sufticient to. pro-l duce a product .of` the same octane level.

The'improvement-.in stability of the present cogelled chromia-alumina/ composites impregnated withrnolybdena' prepared inthe manner herein described. as illus-. trated in the table set forth below using. the. conversion of-.CrzOs to. the*` crystalline form as vthe measure ofthe instability. The test conditions employed involved heating thefcatalyst -at a temperature of 1400" F. in, air for a predetermined 4length of time. Theamount of chromia converted to. the g crystalline fornrwas determinedA by Xaraya ditlractiom The results obtainedewerenas. followsz.,

Y Percent; Time, Crystal- I Hrs. line CrzO Chromia-alumina (32% GMOs-68% AlzO); 10 16 Chromiaalumlna-molybdena (32% @awr-'67.25%

103jr0.75% M0073); t... v 4. 5 l2 Chromia alumina molyb 670%Al303- .M603 4. 5f 9 Chromiajflalumm molybde u 1 61.9%;A1to.-.- 9 o%'-Mao 23 8 The similar cogelled chromia-aluminaV .catalyst It will be noted from the above-tabulated data that the catalyst containing 9.0 percent molybdena showed no appreciable crystalline CrzOa under the same conditions at which chroma-alumina showed 16 percent by weight of crystalline CrzOa. At the more severe test conditions, with an exposure ytime more than twice that of the chromia-alumina, the improved catalyst showed only onehalf the crystalline CrzOs content of the former.

It is to be understood that the above description is merely illustrative of the preferred embodiments of the invention, of which many variations may be made within the scope of `the following claims by those skilled in the art without departing from the spirit thereof.

What is claimed is:

1. A catalytic composite consisting essentially of 10 to 30 percent by weight of chromia, 50 to 89 percent by Weight alumina, and 1 to 2O percent by weight of molybdena, having chromia and alumina components intimately combined in the form of a dried hydrogel, which hydrogel is impregnated with the molybdena component.

2. A catalytic composite consisting essentially of 20 to 30 percent by weight of chromia, 58 to 72 percent by weight of alumina, and 8 to l2 percent by weight of molybdena, having the chromia and alumina components intimately combined in the form of a dried hydrogel, which hydrogel is impregnated with the molybdena component.

References Cited in the le of this patent UNITED STATES PATENTS 1,778,517 Benner Oct. 14, 1930 2,270,165 Groll et al. Jan. 13, 1942 2,397,350 Hayden et al M-ar. 26, 1946 2,451,471 Burke et al Oct. 19, 1948 2,492,167 Marisic et al Dec. 27, 1949 2,577,823 Stine Dec. 11, 1951 2,602,771 Munday et al July 8, 1952 2,635,082 Smith Apr. 14, 1953 2,670,322 Krebs et -al Feb. 23, 1954 

1. A CATALYTIC COMPOSITE CONSISTING ESSENTIALLY OF 10 TO 30 PERCENT BY WEIGHT OF CHROMIA, 50 TO 89 PERCENT BY WEIGHT ALUMINA, AND 1 TO 20 PERCENT BY WEIGHT OF MOLYBDENA, HAVING CHROMIA AND ALUMINA COMPONENTS INTIMATELY COMBINED IN THE FORM OF A DRIED HYDROGEL, WHICH HYDROGEL IS IMPREGNATED WITH THE MOLYBDENA COMPONENT. 